Generally, the widely-used peripheral input device of a computer system includes for example a mouse device, a keyboard, a trackball device, or the like. Via the keyboard, characters and symbols can be inputted into the computer system directly. As a consequence, most users and most manufacturers of input devices pay much attention to the development of keyboards.
FIG. 1 is a schematic top view illustrating the outer appearance of a conventional keyboard. As shown in FIG. 1, there are plural keys 10 on a surface of the conventional keyboard 1. These keys 10 are classified into several types, e.g. ordinary keys 101, numeric keys 102 and function keys 103. When one of these keys 10 is depressed by the user's finger, a corresponding signal is issued to the computer, and thus the computer executes a function corresponding to the depressed key. For example, when an ordinary key 101 is depressed, a corresponding English letter or symbol is inputted into the computer. When a numeric key 102 is depressed, a corresponding number is inputted into the computer. In addition, the function keys 103 (F1˜F12) can be programmed to provide various functions. For example, the conventional keyboard 1 is a keyboard for a notebook computer.
With the maturity of the computing technologies, the keyboard manufacturers make efforts in designing novel keyboards with special functions in order to meet diversified requirements of different users. For this reason, luminous keyboards are favored by users. The outer appearance of the conventional luminous keyboard is substantially similar to the outer appearance of the conventional keyboard 1. Since the luminous keyboard provides the function of illuminating the keys, the inner structure of the luminous keyboard is different from the inner structure of the keyboard without the illuminating function. Hereinafter, the inner structure of the luminous keyboard will be illustrated in more details. FIG. 2 is a schematic cross-sectional view illustrating a conventional luminous keyboard. As shown in FIG. 2, the conventional luminous keyboard 2 comprises plural keys 20, a membrane switch circuit board 21, a light guide plate 22, a backlight module 23, a base plate 24 and a reflecting plate 25. Each key 20 comprises a keycap 201, a scissors-type connecting element 202 and an elastic element 203. From top to bottom, the keycap 201, the scissors-type connecting element 202, the elastic element 203, the membrane switch circuit board 21, the base plate 24, the light guide plate 22 and the reflecting plate 25 of the conventional luminous keyboard 2 are sequentially shown. The backlight module 23 is located at a side of the membrane switch circuit board 21. For example, the conventional luminous keyboard 2 is a keyboard for a notebook computer (not shown).
In the key 20, the keycap 201 is exposed outside the conventional luminous keyboard 2, and thus the keycap 201 can be depressed by the user. The scissors-type connecting element 202 is used for connecting the keycap 201 and the base plate 24. The elastic element 203 is penetrated through the scissors-type connecting element 202. In addition, both ends of the elastic element 203 are contacted with the keycap 201 and the membrane switch circuit board 21, respectively. The membrane switch circuit board 21 comprises an upper wiring plate 211, a separation layer 212, and a lower wiring plate 213. The upper wiring plate 211, the separation layer 212 and the lower wiring plate 213 are all made of a light-transmissible material. The light-transmissible material is for example polycarbonate (PC) or polyethylene (PE). The upper wiring plate 211 comprises an upper printed circuit pattern 2111 with plural upper contacts 2112. The separation layer 212 is disposed under the upper wiring plate 211, and comprises plural perforations 2121 corresponding to the plural upper contacts 2112. The lower wiring plate 213 is disposed under the separation layer 212. Moreover, the lower wiring plate 213 comprises a lower printed circuit pattern 2131 with plural lower contacts 2132 corresponding to the plural upper contacts 2112. The plural lower contacts 2132 and the plural upper contacts 2112 are collectively defined as plural key switches 214.
The backlight module 23 comprises an illumination circuit board 231 and plural light-emitting elements 232. For clarification and brevity, only two light-emitting elements 232 are shown in the drawing. The illumination circuit board 231 is disposed under the membrane switch circuit board 21 and electrically connected with the light-emitting elements 232. The illumination circuit board 231 provides electric power to the plural light-emitting elements 232. The plural light-emitting elements 232 are disposed on the illumination circuit board 231. In addition, the plural light-emitting elements 232 are inserted into plural reflecting plate openings 251 of the reflecting plate 25 and plural light guide plate openings 221 of the light guide plate 22, respectively. By acquiring the electric power, the plural light-emitting elements 232 are driven to emit plural light beams B. Moreover, the plural light beams B are introduced into the light guide plate 22. For example, the plural light-emitting elements 232 are side-view light emitting diodes. The plural light beams B are subjected to total internal reflection within the light guide plate 22, and thus the plural light beams B are guided to the keycaps 201 by the light guide plate 22. As shown in FIG. 2, the base plate 24 is arranged between the membrane switch circuit board 21 and the light guide plate 22. The keycap 201, the scissors-type connecting element 202, the elastic element 203 and the membrane switch circuit board 21 are supported by the base plate 24. The reflecting plate 25 is disposed under the light guide plate 22 for reflecting the plural light beams B. Consequently, the plural light beams B are directed upwardly, and the utilization efficiency of the light beams B is enhanced.
In the conventional luminous keyboard 2, each keycap 201 has a light-outputting zone 2011. The light-outputting zone 2011 is located at a character region or a symbol region of the keycap 201. Moreover, the position of the light-outputting zone 2011 is aligned with the position of a corresponding light-guiding dot 223 of the light guide plate 22. The light beams B can be guided upwardly to the light-outputting zone 2011 by the corresponding light-guiding dot 223. The base plate 24 comprises plural base plate openings 241. The plural base plate openings 241 are aligned with corresponding light-guiding dots 223 and corresponding light-outputting zones 2011. On the other hand, since the membrane switch circuit board 21 is made of the light-transmissible material, the plural light beams B can be transmitted through the membrane switch circuit board 21. Consequently, after the plural light beams B are guided by the light-guiding dots 223, the plural light beams B are sequentially transmitted through the plural base plate openings 241 and the membrane switch circuit board 21 and directed to the plural light-outputting zones 2011, thereby illuminating the character regions or the symbol regions of the keycaps 201. Under this circumstance, the illuminating function is achieved.
However, the conventional luminous keyboard still has some drawbacks. For example, each of the upper printed circuit pattern 2111 and the lower printed circuit pattern 2131 of the membrane switch circuit board 21 is formed by printing plural silver conductor lines. As known, the resistance of silver is high. Moreover, the resistance tolerances of the upper printed circuit pattern 2111 and the lower printed circuit pattern 2131 are very large whenever the membrane switch circuit board 21 is produced. For example, the resistance tolerance is even up to several hundred ohms. For controlling the membrane switch circuit board 21 to generate the stable voltage, it is necessary to adjust the resistance value of the membrane switch circuit board 21 after the membrane switch circuit board 21 is produced. In other words, the use of the conventional membrane switch circuit board 21 increases the fabricating cost.
Therefore, there is a need of providing a luminous keyboard with reduced fabricating cost.